(1) Field of the Invention
This invention relates to a control valve for use in a fluid-pressure operating system, and more particularly to a control valve positioned between a direction-changeover valve and an actuator. Furthermore, this invention is associated with a control valve which may prevent an impulsive operation of an actuator by slowing down the movement of a piston under a meter-in control, such as when no fluid pressure is applied to an actuator at the starting of operation and yet may accelerate the movement of a piston during the operation except for a starting phase of the operation.
(2) Description of the Prior Art
Hitherto, for adjusting the speed of a piston reciprocating within a cylinder in an actuator, a meter-out control system has been adopted for use as a speed controller. However, the meter-out control system poses a problem in that, for instance, after the operation, or inspection of equipment, the pressure within the cylinder remains at an atmospheric pressure level, with the result that the speed control of a piston is possible only when pressure is applied to the controller, and hence the speed control of the piston is disabled in a condition where no pressure is applied. As a result, there often occurs damage to fixtures or injury of an operator. Accordingly, an operator must pay close attention at the commencement of operation, so that efficiency is lowered.
For the aforesaid reasons, the speed controller is used in a meter-on control mode. Although this attempt meets a partial success in preventing impulsive movement of the piston at the starting of operation, there arises the disadvantage that an excessively long time is required until the fluid pressure is built up within the cylinder hence lowering the speed of the piston, so that a delay in transmission of pressure occurs, with an accompanying loss in operation.
It is an object of the present invention to provide a control valve, which insures a safe operational speed for an actuator, without causing a loss in operation.
It is another object of the present invention to provide a control valve which may retard the starting speed of a piston but accelerate the speed of the piston during operation except for the starting phase thereof.